Design over time

The core idea that makes Agile sensible, though, is that good and complex design can be incrementally created through simple, local changes. That’s a new idea, a discovery of the last generation. When birds flock, they fly in complex patterns and formations — but it turns out the birds don’t need a complicated playbook, just some simple rules about following your neighbors. Cell differentiation, it turns out, leverages simple rules as well; there isn’t a big master plan for building a kitten or a kidney, just lots of local rules. People didn’t know this in 1960, just like people didn’t know about evolution in 1860. They know it now.